I bought a Shar Professional quartz metronome for about $24,95. So far, it has lasted about 20 hours on one nine-volt battery.
The only bad thing is the tempos are ...112, 116, 120, 126, 132... These are a little far apart for walking, but 116 or 120 works well for me. If I wanted to slowly increase my stride rate, I'd use the metronome on the Anadroid.